Microencapsulation is a process for completely enveloping tiny masses of solid particles, or liquid droplets in a protective coating which separates the substance from its environment. The use of microencapsulated chemicals for toxicology studies presents a number of advantages including the testing of volatile or chemically reactive compounds in the animal diet, minimization of problems with palatability, etc. Several volatile and/or reactive chemicals have been successfully encapsulated using a starch, gelatin, or gelatin/sorbitol matrix and determined to be stable when mixed with rodent feed. The relative bioequivalence and palatability of microencapsulated trichloroethylene, 1.1.1.-trichloroethane and 2- ethylhexanol in NIH-07 diet has been demonstrated. Reproductive toxicology studies of encapsulated trichloroethylene and 2-ethylhexanol have been successfully completed. Currently, a 14-day and 90-day subchronic feeding study of 1.1.1.-trichloroethane in rats and mice is in progress. Studies continue for the demonstration of the bioequivalence and palatability of microencapsulated cinnamaldehyde, citral, and 1.1.2.2-tetrachloroethane.